I was just planning to just edit it into my first post when I got KS working on Linux, but the turnout was so different this time would be justified to make a second post.
In Ubuntu, it is really bad. Juni moves really choppy, and on the transition to the second room, I first see a bunch of red dots (the tiles under the objects, I guess?) for about a full second. If I press Ctrl+R, Juni's death animation takes about 21 seconds. *gasp*
I'm really surprised, because the computer had no problem with this level in Windows, and other levels that I would expect to lag are running fine in Ubuntu.
Laptop computer
CPU Speed: 2.00 GHz
Memory: 3GB RAM (DDR2)
Graphics: "Mobile Intel(R) 4 Series Express Chipset Family" (with 1293MB on-board memory)
Operating System: Ubuntu 9.10 (Karmic Koala), using Wine 1.1.38